Abstract: Using hrpN of Erwinia amylovora as a radio-active probe, hrpN of Erwinia stewartii was located within its wts cluster. This gene was cloned and mutagenized with Tn5 to get mutants MA1 and MA2. These hrpN mutants were verified by Southern blotting, Western blotting, sequencing and hypersensitive response to make sure that the Tn5 insertions were in the open reading frame of the hrpNEs gene and no truncated harpinEs was produced by these mutants. In order to assess the role of the hrpNEs gene product i.e., harpinEs in the pathogenicity of the bacterium, mutants MA1 hrpN 123 :: Tn5, MA2 hrpN 254 :: Tn5 and DM760 hrpN 189 :: Tn5 were compared to the wild-type strain DC 283 using ED50, disease severity, growth rate in planta and response time as pathogenicity parameters. The ED50 of the mutants was not significantly different (p=0.05) from that of the wild-type. The differences between the response times for mutants and the wild-type were not statistically significant (p=0.05) either. The mutants grew and caused as severe disease in the corn seedlings as the wild-type did. The results indicated that the mutations in the hrpN did not affect the pathogenicity of E. stewartii in any way i.e. the mutants were neither qualitatively nor quantitatively different from the wild-type controls.